Connector for explosive cords



Sept. 14, 1965 J. COULSON CONNECTOR FOR EXPLOSIVE CORDS Filed Aug. 2,1963 INVENTOR JOHN R. COULSON United States Patent 3,205,818 CONNECTORFOR EXPLOSIVE CGRDS John R. Coulson, Wayne, NJ., assiguor to E. I. duPont de Nemours and Company, Wilmington, Del., a corporation of DelawareFiled Aug. 2, 1963, Ser. No. 299,603 4 Claims. (Cl. 102-47) Thisinvention relates to a device for effectively and safely securing alength of low energy connecting cord and a detonating fuse in operativerelationship to one another so that a detonation stimulus can bepropagated from the fuse to the cord or, conversely, from the cord tothe fuse.

Recently, a novel detonation transmitting cord, termed low-energyconnecting cord, has been developed. Such cord is described in U.S.Patent 2,982,210 and comprises a continuous core of a detonatingexplosive, e.g., PETN, RDX, nitromannite, HMX, lead azide, picrylsulfone, etc., at a loading of from 0.5 to 2 grains per foot of length,contained within a sheath of a ductile metal which is subsequentlycovered with one or more layers of reinforcing and/ or waterproofingmaterial. Due to its ability to propagate a detonation impulse withoutattendant brisance and because it is free frornthe hazards associatedwith electric initiators, in many explosive applications, such asblasting operations, this cord has replaced conventional detonatingfuse, i.e., Primacord, and electrical initiators. In many applications,it is desirable to use this cord in conjunction with detonating fuse,the low-energy connecting cord being used in sections of the blastingassembly where brisance would be undesirable and the detonating fusebeing used where a detonation stimulus of greater magnitude is neededor, in any case, would not be objectionable. In such assemblies, it isnecessary to secure the ends of the lengths of the low energy connectingcord and the detonating fuse together in abutting relationship so thatthe detonation impulse from one detonation-transmitting means, i.e., thefuse or the cord, will be reliably propagated to the other detonationtransmitting means. Heretofore the ends have been held in the requisiteabutting relationship by metal clips, for example, of the clothespintype, which have not been satisfactory. Not only do clips of this typefail in many cases to hold the cord and fuse in operative arrangement,they provide a unit in which there is a relatively great susceptibilityto accidental actuation by stray electric currents and which willshatter to produce undesirable shrapnel upon detonation.

These and other deficiencies are overcome by this invention whichprovides a connector for explosive cords which comprises a tube of anelectrically nonconductive material having at least one open end, atransverse slot intermediate the ends of the tube and communicating withits bore, the walls of the slot providing means for accepting andengaging a first explosive cord in a recessed position in the tube atsubstantially right angles to its longitudinal axis, and means in saidbore for retaining the end of a second explosive cord in said tube inpropa gating relationship to said first cord.

In a particularly preferred embodiment of this invention, a boostercharge of high velocity detonating explosive is interposed between, andin propagating relationship to, the end of the second cord in the boreof the tube and the slot for the firstcord, the booster charge beingadapted to transmit a detonation stimulus from one of said cords to theother.

The term explosive cord as used herein is meant to include both thenewly developed low-energy connecting cord and conventional detonatingfuse.

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The term transverse slot is intended to require that the slot extendcompletely across the tube at an angle to its longitudinal axis.

The first cord should be recessed sufiiciently to allow propagationbetween it and the second explosive cord or between it and a boostercharge if a booster charge is required. Although it is not essential inall cases, it is preferred that the exposed core of the second cord beessentially in contact with the wall of the first cord. For example, lowenergy connecting cord having a core of PETN will pick up the detonationfrom Primacord if it is flush or nearly flush; however, low energyconnecting cord having a core of 2 gr./ft. lead azide will pick up adetonation from a cord having a cord of PETN at a loading of a 4 gr./ft.contained in a sheath of rayon braid and a polyethylene jacket across aspace of about one inch.

The parts of the connector may be more clearly illustrated by referenceto the accompanying drawings in which:

FIGURE 1 is a view of one form of a connector in accordance with thisinvention in longitudinal cross section;

FIGURE 2 is a perspective view of the assembly with a length ofdetonating fuse and a length of connecting cord inserted;

FIGURE 3 is a view in partial cross-section of an alternative embodimentof the connector of this invention;

FIGURE 4 is a view in partial cross-section of still another embodimentof the connector of this invention; and

FIGURE 5 is an enlarged perspective view of the retaining clip in theconnector of FIGURE 4.

Referring to the drawings in more detail, in FIGURE 1, 1 is a tube of anonconductive material having an open extremity A and a closed extremityB. Slot 2 is provided near extremity B and is essentially perpendicularto the longitudinal axis of the shell. The slot is provided withresilient projections 3 and terminates in recessed channel 4- which ishere shown as circular and which is adapted to receive detonating fusetransversely therethrough. The bore 5 of the tube 1 proceeds from openextremity A and communicates with channel 4 through opening 6. A boostercharge 7 of a high velocity detonating explosive is contained in capsule16 which is crimped to the end of low energy connecting cord 8 withinthe shell and is contiguous to opening 6 which corrnnunicates withchannel 4 provided for the detonating fuse. As may be seen from thepartial cut away view, the low energy connecting cord comprises core 9of detonating composition, metal sheath l0 and .a countering 11 of awaterproof composition. Shoulder projection 17, which may be onecontinuous annular projection or a plurality of individual projections,provides means in the bore which permit forceful insertion of capsule 16from the open end A of tube 1 but resist its withdrawal therebyretaining cord 8 in the bore of tube 1.

In FIGURE 2, the connector of FIGURE 1 is shown with a length ofdetonating fuse 15 in channel 4 and held in place by projections 3. Lowenergy connecting cord is contained in bore 5 of tube 1.

In FIGURE 3, the elements are again as in FIGURE 1, however, in thisembodiment, both ends of the tube are open and therefore slot 2 is bestdefined as terminating in two aligned apertures 4a, one at each of itsends. The alignment of these apertures is such that they position theexplosive cord, e.g., detonating fuse, with respect to booster capsule 7in the same manner as channel 4 (FIGURE 1). In addition, slot 2 isangled to provide greater holding power and one or more ribs 19 areprovided to insure a snug fit between the booster capsule and the innerwall of tube 1. A thin rib or rudder 2t reinforces the slotted portionof the tube and strengthens the grip of the tubular connector on thedetonating fuse. This strengthening also could be accomplished byincreasing the wall thickness or by using a more rigid nonconductivematerial.

In FIGURE 4, the elements are again as in FIGURE 1, however, in thisembodiment the booster charge 7 is a pressed pellet contiguous toopening 6 which communicates between bore and channel 4. Clip 12 isprovided to engage the low-energy connecting cord with its cut end inpropagating relationship to the booster charge 7. The clip hasprojections 13 which extend from its interior surface and cut into thecountering of the low energy connecting cord and an oppositely disposedserrated edge 14 which grips the inner wall of tube 1.

FIGURE 5 is an enlarged perspective view of the clip.

In operation, the low-energy connecting cord is inserted into the boreof the tubular shell so that the cut end of the cord is in propagatingrelationship to the slot for the detonating fuse, either directly orthrough booster charge 7. As shown, booster charge 7 can be contained ina capsule which is crimped to the inserted end of the low-energyconnecting cord or may be a pressed pellet of an explosive composition.When the booster charge is contained in a capsule, the cord may beforcefully inserted into the bore of the tube past shoulder projections17 with the capsule containing the booster charge already crimped on theend of the cord. Alternatively, in embodiments where the tube is open atboth ends, as in FIGURE 3, the cord is inserted into the bore of thetube past shoulder 17, i.e., the tube may be slipped over the cord, thecapsule containing the booster charge crimped on the end of the cord andthe capsule positioned in the bore of the tube with the shoulder 17 andthe rib I9 retaining the cord in the bore of the tube. The detonatingfuse is inserted into slot 2 which preferably is flared for easyinsertion of the fuse and is pulled down past resilient projections 3which retain the fuse in aperture 4. According to the requirements ofthe blasting assembly, either the detonating fuse or the low-energyconnecting cord can be the main line, the other cord then being thebranch line. In situations in which the low-energy connecting cord isused as the main line, the detonation impulse is propagated to boostercharge 7 by the explosive core 9 of cord 8. When booster charge 7 isinitiated, the detonation impulse produced is suflicient to initiate thedetonating fuse. On the other hand, if the detonating fuse is the mainline, the brisance of this fuse, as a detonation impulse passes throughopening 6, initiates the core 9 of cord 8 directly so there is no needfor a booster charge.

The connector of this invention is particularly useful in nonelectricdelay blasting assemblies which provide insurance from cut offs due toground movement and also permit bottom hole priming while avoiding thehazards of accidental actuation by stray electric currents, e.g.,electrostatic discharges, radio frequency energy, and stray currentsencountered with electric initiators. Since shell 1 is of anelectrically nonconductive plastic material, there is no danger ofaccidental, premature initiation of the assembly due to the build-up ofcharges or instantaneous surges of electricity through the unit.Disintegration of the plastic material of the shell upon detonation ofthe cords is not hazardous to persons or equipment in the vicinity.

The tubular nonconductive shell which is critical to our invention musthave sufficient flexibility to enable the cords to be connected withrelative ease yet must be rigid enough to withstand pressures andabrasive action present in blasting operations. Accordingly, plasticmaterials such as high density polyethylene, polypropylene, acetalresins, polytetrafiuoroethylene, nylon, unplasticized polyvinylchloride, polystyrene, acrylic polymers, and phenolic resins havingcharacteristics of rigidity, tear resistance, and a flexibility aresuitable for use as tube 1. These materials are particularly suitablebecause of their high resistance to sear and deterioration in outsideuse. The shell of the connectors can be machined or, preferably, formedby injection molding.

The booster charge present to insure initiation of the receptor chargeis a pressed, high velocity detonating explosive, for example a pelletof pressed waxed RDX or a pellet of pressed pentolite or a similarcomposition. Placing the booster charge in a tubular capsule, which isattached, e.g., by crimping, to the end of the low energy connectingcord, insures against damage to the ends of the cord and maintains awaterproof seal at the ends. The loading of the booster charge willpreferably be about 1.5 to 2.0 grains. A booster charge of 1.8 grains offinely divided PETN in a coined bottom shell is particularly preferred.

Many variations of the above described assembly are within the scope ofthe invention. It is intended therefore to be limited only by thefollowing claims.

What is claimed is:

1. In combination, a connector comprising an electrically-nonconductivetube having a substantially cylindrical bore extending its entirelength; a transverse slot for accepting a length of detonating fuse,extending through the side of the tube intermediate its ends in adirection generally normal to the bores longitudinal axis andterminating in two aligned apertures, one at each end of the slot, thealignment being such that a straight line connecting the aperturesintersects the longitudinal axis of said bore at substantially rightangles, and the Walls of said slot providing resilient projections forpositioning and firmly engaging said fuse in said apertures; reinforcingmeans integral with the exterior surface of said tube opposite said slotand extending in the direction of said longitudinal axis; a singlelength of low-energy connecting cord extending into said bore throughits first end; and a. booster capsule snugly seated in said bore andhaving an integrally closed extremity contiguous to the side of saidapertures nearest the bores said first end, said capsule containing abooster charge at its closed extremity in propagating relationship tothe end of said cord in the bore and having its other extremity crimpedon said cord; the said first end of the bore being provided with atleast one integral projection for abutting the crimped extremity of thecapsule and preventing its withdrawal from said first end, said borebeing of sufficient diameter from its second end to said projection atits other end to permit insertion of said capsule into the bore throughsaid second end and its passage past the slot until said integrallyclosed extremity is contiguous to said nearest side of the apertures.

2. The combination of claim 1 wherein the detonating fuse is firmlyengaged in said apertures in propagating relationship to said boostercharge.

3. In combination, a connector comprising an electrically-nonconductivetube closed at one end and having a substantially cylindrical boreextending through its other end and running part of its length; atransverse slot between said closed end and the internal end of saidbore for accepting a length of detonating fuse, said slot extendingthrough a side of the tube in a direction generally normal to the boreslongitudinal axis and terminating in a channel which communicates withsaid bore and intersects said axis at substantially right angles, thewalls of said slot providing at least one resilient projectionintermediate said channel and the outside surface of the tube forpositioning and firmly engaging said fuse in said channel atsubstantially right angles to said axis; a single length of low-energyconnecting cord extending into said bore through its open end; and abooster capsule snugly seated in said bore and having an integrallyclosed extremity adjacent to the side of said channel nearest the boresopen end, said capsule containing a booster charge at its closedextremity in propagating relationship to the end of said cord in thebore and having its other extremity crimped on said cord; the open endof said bore being provided with at least one integral projecting meansfor permitting forceful insertion of said crimped capsule into the bore,said means abutting the crimped extremity of the inserted capsule andresisting its withdrawal from the bore, and said booster charge withinthe inserted capsule being in propagating relationship to said channel.

4. The combination of claim 3 wherein the detonating fuse is firmlyengaged in said channel in propagating relationship to said boostercharge.

References Cited by the Examiner UNITED STATES PATENTS 1,021,934 4/12Kellogg 102-27 2,587,694 3/52 Chalmers et al 102-27 2,715,365 8/55Godchaux et a1. 10227 2,952,206 9/60 Becksted 10227 3,020,844 2/62Miller 10227 FOREIGN PATENTS 741,868 12/55 Great Britain.

SAMUEL FEINBERG, Primary Examiner. SAMUEL W. ENGLE, Examiner.

3. IN COMBINATION, A CONNECTOR COMPRISING AN ELECTRICALLY-NONCONDUCTIVETUBE CLOSED AT ONE END AND HAVING A SUBSTANTIALLY CYLINDRICAL BOREEXTENDING THROUGH ITS OTHER END AND RUNNING PART OF ITS LENGTH; ATRANSVERSE SLOT BETWEEN SAID CLOSED END AND THE INTERNAL END OF SAIDBORE FOR ACCEPTING A LENGTH OF DETONATING FUSE, SAID SLOT EXTENDINGTHROUGH A SIDE OF THE TUBE IN A DIRECTION GENERALLY NORMAL TO THEBORE''S LONGITUDINAL AXIS AND TERMINATING IN A CHANNEL WHICHCOMMUNICATES WITH SAID BORE AND INTERSECTS SAID AXIS AT SUBSTANTIALLYRIGHT ANGLES, THE WALLS OF SAID SLOT PROVIDING AT LEAST ONE RESILIENTPROJECTION INTERMEDIATE SAID CHANNEL AMD THE OUTSIDE SURFACE OF THE TUBEFOR POSITIONING AND FIRMLY ENGAGING SAID FUSE IN SAID CHANNEL ATSUBSTANTIALLY RIGHT ANGLES TO SAID AXIS; A SINGLE LENGTH OF LOW-ENERGYCONNECTING CORD EXTENDING INTO SAID BORE THROUGH ITS OPEN END; AND ABOOSTER CAPSULE SNUGLY SEATED IN SAID BORE AND HAVING AN INTEGRALLYCLOSED EXTREMITY ADJACENT TO THE SIDE OF SAID CHANNEL NEAREST THEBORE''S OPEN END, SAID CAPSULE CONTAINING A BOOSTER CHARGE AT ITS CLOSEDEXTREMITY IN PROPAGATING RELATIONSHIP TO THE END OF SAID CORD IN THEBORE AND HAVING ITS OTHER EXTREMITY CRIMPED ON SAID CORD; THE OPEN ENDOF SAID BORE BEING PROVIDED WITH AT LEAST ONE INTEGRAL PROJECTING MEANSFOR PERMITTING FORCEFUL INSERTION OF SAID CRIMPED CAPSULE INTO THE BORE,SAID MEANS ABUTTING THE CRIMPED EXTREMITY OF THE INSERTED CAPSULE ANDRESISTING ITS WITHDRAWAL FROMN THE BORE, AND SAID BOOSTER CHARGE WITHINTHE INSERTED CAPSULE BEING IN PROPAGATING RELATIONSHIP TO SAID CHANNEL.